....well, you've hit the nail right on the head with your own answer.
Those discerning car buyers who want a decent car and don't mind paying fair prices, spend their cash on other makes. Those that simply want a vehicle "with a brilliant deal" will go for the likes of Fiat...who wouldn't shift many cars at all in the UK, if it weren't for offering them through "schemes" at bargain-basement prices....hence their terrible depreciation.